The present invention relates to an electrically-operated multi-needle chisel tool including a number of needle chisels extending from the forward end of the tool which are adapted to be vigorously moved to and fro to remove the rust from metal surfaces, weld spatters, foundry sand and the like or to grind the surfaces of stone and concrete materials.
As disclosed in Japanese Patent Application Publication No. 42-5512 (1967), the electrically-operated multi-needle chisel tool generally comprises a housing having a front portion and a rear portion, an electric motor mounted in said rear portion, a cylinder means extending forwardly from the front portion of the housing, a piston disposed in said cylinder means and adapted to be reciprocated by a linear motion being converted from the rotary motion of said motor by means of a motion conversion mechanism such as a crank mechanism or an eccentric mechanism, an anvil disposed so as to be hit by said piston, a needle supporter for supporting a number of needle chisels for axially slidable movement, and a return compression spring for returning the needle supporter, said piston, said anvil and said needle supporter being adapted to be synchronously reciprocated by means of said motor.
With this type of chisel tool, the electric motor is energized to reciprocate the piston. As the piston advances, it strikes the anvil which in turn hits the needle chisels and the needle supporter to cause the tips of the chisels to work on the surfaces of stone, metal or the like. In such a conventional tool, however, an extremely violent reaction is brought about during the grinding operation, since the motion conversion mechanism of the drive motor is connected in series with the piston to form a serially connected rigid unit. This results in the following disadvantages:
Such a violent reaction gives a great impact directly to the neighboring parts, particularly the electric drive means, resulting in loosening, rattling and/or misaligning of the properly assembled parts to thereby impede smooth operation of the tool. In addition, the various parts of the tool can be adversely affected and may even break down. Especially due to the direct coupling between the electric motor and the motion conversion mechanism, a large reaction causes excessive wear on the rotating and sliding portions of the parts, resulting in greatly reducing the useful life of the tool. Such reaction, as it is naturally transmitted to the hands of the operator, will also fatigue him and be injurious to his health. Moreover, if the operator should accidentally turn on the power switch for the electric motor with the tips of the needle chisels bearing against the surface of stone or metal to be worked on, the components including the chisels, anvil, piston and the motion conversion mechanism would form a single serially interconnected rigid body which would rapidly retract the entire tool toward the operator to subject him to a dangerous reaction.